The invention relates to an electrolytic foil capacitor comprising a capacitor roll which is impregnated with electrolyte liquid, which capacitor roll is accommodated in a metal housing which is open at one end and which is sealed in a gas-tight and liquid-tight manner at the open end by a flat, metal cover which is provided with an elastic sealing ring.
An electrolytic capacitor of the type mentioned in the opening paragraph is known from the published German Patent Application DE-OS 28.05.644. In said Patent Application a description is given of a capacitor having a cylindrical housing which is closed by means of a metal cover. The round cover is circumferentially provided with an elastic sealing ring. In the housing there is provided a circular, inwardly directed ridge on which the cover rests via the sealing ring. As the edge of the housing is flanged in such a manner that it presses on the cover, the cover engages the circular ridge in the housing in a clamping manner via the sealing ring. The exerted clamping force extends predominantly in the axial direction. By means of said construction a gas-tight and water-tight housing is obtained.
The known capacitor has disadvantages. When the seal described therein is provided in electrolytic foil capacitors of small dimensions, such as SMD-capacitors, no optimum sealing is obtained. This is particularly true when these capacitors are mounted on a printed circuit board. During the soldering of such a SMD-capacitor an overpressure is formed in the capacitor as a result of the relatively high temperature used. Owing to this, the cover may be pressed off the ridge and, consequently, leakage may occur. This problem cannot be solved entirely by flanging the edge of the housing against the cover. Besides, the flanging of housings is very difficult when the dimensions of the currently customary SMD-electrolytes are taken into account. This is particularly true when the outside of the housing must be beam-shaped. In this case, the wall of the beam-shaped housing must be relatively thick.